It's correct, the brackets are just different:
2.5mm2 = 2.5(mm^2) not (2.5mm)^2.Mathematically speaking the way it's written would be interpreted as ax^2 since the power takes precedence over the multiplication, not (ax)^2. So it's fine to say 2.5mm2. If you wanted 2.5 x 2.5 you would have to make that explicit.
Theo
The key is that "2.5mm squared" is not the same as "2.5mm square"
But "2.5 square mm" is unambiguous.
Things could easily have changed but early panel cabling was expected to carry the maximum short circuit current a panel array could produce without hazard.
2.5 millimetres squared is a perfectly valid measure for something of *any* shape with a cross sectional area equal to that of a square measuring 2,5mm on each side but this is a considerably larger area than that of a conductor in a 2.5mm^2 T&E cable conventionally used for a 30 amp ring main. And for educators (e.g. the guys on Efixx) to use this term is wrong, they should say "square millimetres".
The square root of 2.5 is 1.58 so a 2.5mm^2 conductor has an area equal to 1.58 millimetres squared.
The NPL defines the SI symbol for the basic derived unit of area as m^2 with the name 'square metre' and *not* 'metre squared'
I an going to say it is ambiguous. 2.5mm square, or squared implies a square conductor and nothing about it's equivalence.
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Quite, so best keep to convention and not muddy the water.
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